1. Field of the Invention
The apparatus of this invention resides in the area of blast machines and more particularly relates to a shot removal system of a blast machine which propels shot at metal sheets or plates in order to clean them so that they are in suitable condition for further processing.
2. Description of the Prior Art
Blast machines have been used in the prior art to clean sheets, strips and plates of metal, some of which may initially be provided in the form of rolls or coils, for cleaning and descaling by delivering such workpieces on conveyors through long chambers which have shot blast wheels disposed above and below the sheet metal being cleaned. Such prior art machines have provided a plurality of shot blast wheels disposed in such long chamber through which the sheet is passed wherein each shot blast wheel cleans a specific portion of the upper or lower surface of the sheet.
Since many of the prior art chambers are as long as 20 feet, the accumulation of shot on the top surface of the sheet is considerable and must be removed from the sheet as it exits the blast chamber for further processing.
In the prior art several processes have been used to try to remove the shot from the top of the sheet. One method incorporates a series of brushes that sweep parallel to the direction of movement of the metal sheet, which method attempts to brush the shot off the sides of the metal sheet. This removal method has been found to be inefficient with shot still remaining on top of the metal sheet as the sheet passes out of the chamber. The presence of such shot on top of the metal sheet is undesirable as it interferes with further processing of the workpiece. Another method which has been utilized in the past to remove such shot provides for blowers located at the exit of the chamber which blow the shot back into the chamber in line with, but in the opposite direction to, the flow of the workpiece. These blowers attempt to blow the shot off the top of the metal sheet. This method also has proven to be less than 100% effective in that many times more shot will be deposited and left on top of the steel sheets than the blowers can effectively remove. Such blowers will sometimes blow shot back into the path of oncoming shot from the blast wheels thereby interfering with effective cleaning of the metal sheets.